For corn, optimum seed germination occurs when soil temperatures reach 10°C. So is it better to plant corn into cold soils realizing the seed may sit there until the soil warms up? Or should corn be planted when soil temperatures are warmer and approaching 10°C?
Planting into cold soils. Early planting is a well-known component of successful corn production, especially in Manitoba where getting the seed into the ground as early as possible is critical to maximize yield, obtain high quality and low percent kernel moisture at harvest (which will decrease drying costs), and to ensure the crop is mature before fall frosts.
While cooler temperatures alone are not likely to impose a stress on germinating seeds, it can delay the crop’s emergence. Wet conditions added to cold temperatures following planting can also favor development and activity of some soil pathogens that can produce disease stress in both germinating seeds and young seedling. When planting early in the season or when the soil is cold, a planting rate 10% higher than the desired final stand should be considered to compensate for possible increased seedling mortality.
When facing cool planting conditions, other components of successful corn production become more important, such as seedbed condition and planting operations (including planting depth). It is important to keep in mind that rushing the planting operation and planting under less than ideal conditions just to get the crop in can cause other problems that can reduce corn yield potential.
Seed Bed Preparation. When preparing the seedbed, producers should try to perform tillage operations only when necessary and under the proper soil conditions. If facing drier than normal soil conditions, try to reduce secondary tillage passes. If secondary tillage operations are needed, perform only when necessary to prepare an adequate seedbed.
Planting Depth. Under most conditions, a planting depth of 1.5 to 2 inches is recommended. When soil temperatures are lower and when soil moisture levels are adequate, producers may want to target planting depths around 1.5 inches. However, it is recommended not to plant less than 1.5 inches deep as some seed may end up much shallower due to variation in the seedbed and/or normal variation in planting depth that occurs. These shallower plantings can result in poor nodal root development that leads to ‘rootless’ and ‘floppy’ corn problems, as well as uneven emergence or reduced stands.
If it’s still early and soil temperatures are cool but soil moisture is on the drier side, it is not a good idea to plant deeper to chase that soil moisture. Normally good contact between the seed and soil is needed for the seed to take up enough water to allow it to swell and germinate (corn must absorb 30% of its weight in water to germinate). However, planting deeper than 2 inches, especially when soils are cold (i.e., early season, cool season, no-till, etc.), can significantly delay emergence and impact stand establishment.
Final Notes. So let’s answer the questions asked at the start: Is it better to plant into cold soils realizing the seed is going to sit there until the soil warms up? Or should corn be planted when soil temperatures are warmer and approaching 10°C?
Ultimately, the decision on when to plant comes down to each individual farmer and the year. Under most circumstances, the best time to begin planting corn in Manitoba is as early as weather conditions allow you to plant into good seedbed conditions. Hybrids and seed treatments available in today’s corn production systems offer some protection from planting into cooler soils. If planting under less than ideal conditions, adjust the planting operation accordingly. What is important for farmers to remember is regardless of when they start planting mistakes made during the planting operation can put a “ceiling” on the crop’s yield potential.
Last Revised: April 2017